Cull zero homogeneous vertex positions before rasterization

Fix Playroom top right artifact on Nvidia by clipping zero-position vertices.

src/common/logging/log.cpp

@@ -129,6 +129,14 @@ static void WriteImpl(std::string_view text, fmt::text_style style = {}) {
 	}
 }
 
+void WriteToConsoleAndLog(std::string_view text) {
+	WriteImpl(text);
+	if (g_initialized && g_direction != Direction::Console) {
+		WriteStdout(text);
+	}
+	Flush();
+}
+
 void WriteFatal(std::string_view text) {
 	if (g_direction == Direction::Silent || !g_initialized) {
 		WriteStdout(text);

src/common/logging/log.h

@@ -25,6 +25,7 @@ Direction GetDirection();
 bool      IsSilent();
 void      Write(std::string_view text);
 void      Write(fmt::text_style style, std::string_view text);
+void      WriteToConsoleAndLog(std::string_view text);
 void      WriteFatal(std::string_view text);
 void      WriteFatal(fmt::text_style style, std::string_view text);
 void      Flush();

src/graphics/host_gpu/renderer/pipeline/pipelineCache.cpp

@@ -89,12 +89,7 @@ template <typename... Args>
 void PipelineCacheLog(fmt::format_string<Args...> format, Args&&... args) {
 	auto message = fmt::format(format, std::forward<Args>(args)...);
 	message += '\n';
-	if (Log::GetDirection() != Log::Direction::Console) {
-		std::fwrite(message.data(), 1, message.size(), stdout);
-		std::fflush(stdout);
-	}
-	Log::Write(message);
-	Log::Flush();
+	Log::WriteToConsoleAndLog(message);
 }
 
 bool ReadShaderGuestMemory(void*, uint64_t address, uint32_t* value) {

src/graphics/shader/recompiler/backend/spirv/spirvEmitterFlow.cpp

@@ -1,6 +1,9 @@
 #include "graphics/shader/recompiler/backend/spirv/spirvEmitterInstructions.h"
 
+#include "common/logging/log.h"
+
 #include <algorithm>
+#include <atomic>
 
 namespace Libs::Graphics::ShaderRecompiler::Spirv::Emitter {
 namespace {
@@ -500,6 +503,31 @@ void EmitSetAttribute(ValueEmitContext& ctx, const IR::Inst& inst) {
 			state.builder.AddFunction(spv::OpStore, MeshOutputPointer(state, kind, exp.index),
 			                          value);
 		} else if (exp.kind == IR::ExportTargetKind::Position) {
+			if (state.invalid_position_clip_distance != UINT32_MAX) {
+				const auto zero = state.builder.Constant(spv::OpConstantNull, TypeF32Vector(state, 4));
+				const auto equal = state.builder.AllocateId();
+				const auto invalid = state.builder.AllocateId();
+				const auto distance = state.builder.AllocateId();
+				const auto distance_pointer = state.builder.AllocateId();
+				state.builder.AddFunction(spv::OpFOrdEqual, TypeBoolVector(state, 4), equal,
+				                          value, zero);
+				state.builder.AddFunction(spv::OpAll, TypeBool(state), invalid, equal);
+				// Zero at valid vertices makes a primitive containing an invalid position
+				// collapse to its remaining edge, before the undefined 0/0 perspective divide.
+				state.builder.AddFunction(spv::OpSelect, TypeF32(state), distance, invalid,
+				                          ConstantF32Value(state, -1.0f),
+				                          ConstantF32Value(state, 0.0f));
+				state.builder.AddFunction(
+				    spv::OpAccessChain, TypePointer(state, spv::StorageClassOutput, TypeF32(state)),
+				    distance_pointer, state.clip_distance_variable,
+				    ConstantU32(state, state.invalid_position_clip_distance));
+				state.builder.AddFunction(spv::OpStore, distance_pointer, distance);
+				static std::atomic_bool logged = false;
+				if (!logged.exchange(true, std::memory_order_relaxed)) {
+					Log::WriteToConsoleAndLog(
+					    "Shader: emitted zero-position clip guard\n");
+				}
+			}
 			const auto pointer = state.builder.AllocateId();
 			state.builder.AddFunction(
 			    spv::OpAccessChain,

src/graphics/shader/recompiler/backend/spirv/spirvEmitterInternal.h

@@ -116,6 +116,7 @@ struct EmitterState {
 	uint32_t                   per_vertex_variable                   = 0;
 	uint32_t                   point_size_variable                   = 0;
 	uint32_t                   clip_distance_variable                = 0;
+	uint32_t                   invalid_position_clip_distance        = UINT32_MAX;
 	uint32_t                   cull_distance_variable                = 0;
 	uint32_t                   layer_variable                        = 0;
 	uint32_t                   viewport_index_variable               = 0;

src/graphics/shader/recompiler/backend/spirv/spirvEmitterModule.cpp

@@ -476,6 +476,15 @@ void DefineOutputs(EmitterState& state) {
 		DefineMeshOutputs(state);
 		return;
 	}
+	if (state.program.stage == ShaderType::Vertex && clip_distance_count + cull_distance_count < 8u &&
+	    std::ranges::any_of(state.outputs, [](const OutputBinding& output) {
+		    return output.kind == IR::StageOutputKind::Position;
+	    })) {
+		// Reserve one plane for the enabled PA_CL_CLIP_CNTL clipping-error cull.
+		state.invalid_position_clip_distance = clip_distance_count++;
+		state.outputs.push_back({{IR::StageOutputKind::ClipDistance,
+		                          state.invalid_position_clip_distance, 0, "gl_ClipDistance"}});
+	}
 	const auto BuiltIn = [&](uint32_t& variable, uint32_t type, const char* name,
 	                         spv::BuiltIn builtin) {
 		if (variable == 0) {